Trouble with the plastic one is that what security at one airport might pass as OK does not guarantee that you will get the same reaction at all airports.

As it's not an essential item to wear on a plane in any case I would always err on the side of caution knowing that at least I would get to keep it for wearing in future rather than seeing it confiscated.

My friend Andrew forgot to pack his kilt pin when we were flying back from Edinburgh Airport but was allowed through - very lucky in my opinion as most places would have confiscated it.

I was lucky too in June - unknowingly my real sgian was in my kilt jacket pocket which I took off to put through the machine at Cardiff and retrieved when I had gone through the portal. I did not discover this until I had arrived in Barcelona! I was lucky not to have lost it but also perturbed that this was not picked up at Cardiff Security as I wore the jacket on the plane and was therefore potentially an armed threat even though I was not aware of it until afterwards! Makes you wonder how much of a lottery it can be as to what gets through! I made sure it was in my hold luggage for my return flight!